NBSIR 79-1917

Solar Energy Systems—Standards

for Rubber Hose

i

Robert D. Stiehler

‘ John L. Michalak ii

Structures and Materials Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

October 1979

Issued November 1979

—QC

100

.U56

79-1917

^ 1979

US. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
1
NBSIR 79-1917

SOLAR ENERGY SYSTEMS--STANDARDS

FOR RUBBER HOSE

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JUL 2 1 1980

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19-I9n

Robert D. Stiehler

John L. Michalak

Structures and Materials Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

October 1 979

Issued November 1979

U.S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Jr., Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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SOLAR ENERGY SYSTEMS--STANDARDS FOR RUBBER HOSE

Robert D. Stiehler

John L. Michalak

ABSTRACT

A study of commercial rubber hose was made to develop standards for hose

used in solar energy systems. Twelve hoses were evaluated by cycling

between temperatures of about 100“C and temperatures as low as -40°C

during a period of about seven months. Laboratory tests for bursting

strength, compatibility with metals, compression set, ozone resistance,

and water vapor transmission were also made.

The results of this study and tests are presented. Based on these findings, a standard for rubber hose used in solar energy systems is proposed.

iii
TABLE OF CONTENTS

Page

ABSTRACT 1 X

X

LIST OF TABLES . o v LIST OF FIGURES . . . . . » . . . , . v

1. INTRODUCTION ... 1

1.1

1.2

Background

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2. PROBLEM ASSESSMENT 2

2.1 Performance Requirements ..o<.....«.o...ooo... ........... 2 2.2 Properties 2 2.3 Tests 3

3. LABORATORY STUDIES

3.1 Ma terxals ......o....... ..................... ...o....... 3

3.2 Evaluation of Hose Performance ......................... 5 3.3 Ozone Resxstance ...o........................ ........... 10

3.4 Compression Set 10

3.5 Water Vapor Transmission 12

3.6 Bursting Pressure 14

4. DISCUSSION

5. PROPOSED STANDARD

6. ACKNOWLEDGMENT ...

7. BIBLIOGRAPHY .....

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APPENDIX

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30

XV
LIST OF TABLES

Page

1. ASTM Standards Applicable for Testing Hose A

2. Hose Dimensions, Specimen Failures and

Leaks at Clamps 9

3. Compression Set 13

A. Water Vapor Transmission at 100°C 15

5. Effect of Hose on Metal Plugs in Water Vapor

Transmission Tests (166 hours at 100°C) 16

6. Bursting Pressures 18

LIST OF FIGURES

1. Schematic of Circulating System 6

2. Compression Clamp 11

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1 . INTRODUCTION

1.1 BACKGROUND

Rubber hose is used extensively in solar energy systems to connect

solar collectors to manifolds and to connect other components in these

systems. It is a vital link since failure of a hose makes the system

inoperable until replaced. Hose has several advantages for making these

connections; namely,

(1) Rubber hose is flexible and thereby easily accommodates some misalignment of components to be connected.

(2) Rubber hose does not place high stresses on the components to

be connected.

(3) Rubber hose absorbs vibration arising from pumps, motors, etc.

(A) Rubber hose dampens sound transmission and thereby makes a quieter operating system.

(5) Rubber hose is economical to use.

On the negative side, rubber hose has the following disadvantages:

(1) Leakage at the hose connections frequently occurs.

(2) The life expectancy of rubber hose in the severe environment

of solar energy systems is uncertain. Temperatures range from

midday summer temperatures near 100®C and cold winter temperatures of -40°C in some locations. Ozone and atmospheric pollutants are other environmental factors.

(3) Maintenance and replacement of rubber hose between the

collectors and manifolds are generally difficult and costly.

(4) Rubber hose may not be compatible with the fluid used for

heat transfer or the materials to which it is connected.

(5) Rubber hose is not suitable for use above certain temperatures;

these temperatures depend on the type of rubber and reinforcement in the hose.

Thus, there is need for development of standards to overcome these disadvantages and to capitalize on the advantages of using rubber hose.

Some standards exist for rubber hose used in specific industries; for

example, automotive, food, petroleum and railroad. Generally, these

standards are not suitable for hose used in solar energy systems.

1
primarily from the aspect of durability under the severe conditions

encountered. Some standards for testing hose are applicable; for

example, ASTM D 380 Standard Methods for Testing Rubber Hose [1].^'

ASTM D 3832, Standard Specification for Rubber Seals Contacting Liquids in

Solar Energy Systems, is also helpful in developing a standard for rubber

hose. This standard is based on a study of rubber seals for solar energy

systems reported in NBSIR 77-1437 [2].

1.2 OBJECTIVES

This study had the following objectives:

(1) To identify performance requirements for rubber hose used in

solar energy systems

(2) To identify and assess existing test methods for rubber hose

and modify the methods or develop new methods as needed.

(3) To evaluate commercially available hose in the laboratory and

obtain data needed to recommend specific requirements and

tests.

(4) To prepare draft standards for rubber hose for consideration

by ASTM as consensus standards.

2. PROBLEM ASSESSMENT

2 . 1 PERFORMANCE REQUIREMENTS

The primary function of rubber hose used in solar energy systems is to

transport the heat transfer fluids between components without leakage.

The hose must perform this function when initially installed and after

long term exposure to service conditions. In particular, hose should

resist deterioration resulting from exposure to elevate temperatures,

air, ozone, air pollutants such as oxides of nitrogen and sulfur, heat

transfer fluid, etc. The hose should be functional at high operating

temperatures and low night temperatures in winter. The hose should not

contaminate the heat transfer fluid or corrode the materials to which

it is connected.

2.2 PROPERTIES

The following properties are important to assess the quality of materials

and performance:

2.2.1 Tens lie strength and ul timate elongation of the inner 1 iner and

outi'r rubber cover are properties conventionally used to assess quality

1 Numbers in brackets

end of this report.

refer to references in the Bibliography at the

2
of rubber vul canizateso Ultimate elongation is particularly important

since failure occurs in any part of the hose where the ultimate elongation is exceeded during flexing.

2.2.2 Flexibility at low temperatures is essential to withstand low

winter temperatures without failure.

2.2.3 Fluid compatibility is essential to prevent excessive swelling

and degradation of the inner tube. It is assessed by measuring the

change in volume, tensile strength, ultimate elongation and hardness

resulting from immersion in the fluid.

2.2.4 Resistance to air aging is needed for a long service life. It

is assessed by determining the tensile strength before and after conditioning the inner tube and outer rubber cover at elevated temperatures

for a specified time. The change in these properties can provide an estimate of the expected life of the rubber portions of the hose [3].

2.2.5 Resistance to ozone is essential for the rubber cover. Small

amounts of ozone in the atmosphere cause the rubber cover to crack

and subsequently the hose to fail. This phenomenon is distinct from

the oxidation in air at elevated temperatures noted in 2.2.4.

2.2.6 Vapor transmission of the hose should be low to minimize loss

of heat transfer fluid through the walls of the hose in service and

to maintain an efficient system and operation.

2.2.7 Compression set of the hose assesses effectiveness of clamps

in preventing leakage at the end connections.

2.2.8 Bursting pressure must be adequate to withstand the fluid

pressures in the system and to provide an adequate margin of safety.

2.2.9 Reinforcement fiber is the component of a hose that mainly determines the bursting pressure. The fiber should not be affected by the

heat transfer fluid at service temperatures.

2.3 TESTS

Table 1 lists ASTM tests available for assessing some of the properties

mentioned in 2.2. Tests for the other properties are described in the

next section on laboratory studies.

3. LABORATORY STUDIES

3.1 MATERIALS

Eleven commercial rubber hoses and one poly tetrafluorethylene (PTFE) hose

with stainless steel fibrous braid were included in the laboratory study.

These hoses were not designed for use in solar energy systems.

3
Table 1. ASTM Standards Applicable for Testing Hose [1]

D 380 Methods for Testing Rubber Hose

D 395^ Test for Rubber Property - Compression Set

D 412 Test for Rubber Properties in Tension

D 47 1 Test for Rubber Properties - Effect of Liquids

D 573 Test for Rubber Deterioration by Heating in Air Oven

D 1149^ Test for Rubber Deterioration - Surface Ozone Cracking

in a Chamber (Flat Specimen)

D 1349 Rubber - Standard Temperatures and Atmospheres for Testing

and Conditioning

D 2769^ Method of Testing Rubber Hose Used for Liquified Petroleum

Gas - Extractable Material and Vapor Transmission

^ Requires modification of compression assembly and specimen.

^ Requires modification of specimen.

^ Requires modification of testing conditions and procedure.

4
The hoses were made by seven manufacturers from the following types of

rubber:

2 CR Chloroprene rubber (neoprene)

EPDM Terpolymer of ethylene, propylene, and a diene

VMQ Silicone rubber having both methyl and vinyl groups on the

polymer chain.

The type of reinforcement fiber used in the hoses was not obtained for some hoses, but it appeared that rayon was used in the EPDM hoses. The

VMQ hoses had fiber glass or aramld fiber reinforcement.

There were in the study one CR hose, seven EPDM hoses and three VMQ hoses.

All hoses had a nominal 16 mm (5/8 in) bore, except one EPDM hose which

had a nominal 20 mm (3/4 in) bore. A high resilience EPDM hose was received near the end of the study. The only tests made on this hose

were compression set, water vapor transmission, and bursting strength.

3.2 EVALUATION OF HOSE PERFORMANCE

The main part of the study consisted of developing an apparatus for

assessing performance of rubber hose and circulating a glycol water mixture through the twelve hoses for a period of more than seven months,

cycling the temperature of the fluid from about lOO^C to as low as -40®C.

3.2.1 Apparatus

The apparatus consisted essentially of two circulating systems mounted

in an enclosure. One system was constructed of steel and stainless

steel. The other system was constructed of brass and copper.

A schematic diagram of the circulatory system is shown in Figure 1. It

consists of two manifolds between which the 16-mm hoses are connected in

the form of a loop. Each loop consists of two specimens of the same

hose; each specimen is about 350 mm in length. One specimen is connected

to the inlet manifold and the other is connected to the outlet manifold.

The specimens are joined at the other end with a U-shaped fitting to

which a mass is fastened. The fitting and mass exert a force of about

30 N with steel fittings and about 25 N with copper fittings. Four types

of clamps connect the two specimens to the manifolds and U-fitting;

namely, a banded clamp (C-1), a screw clamp (C-3), a screw clamp with

Internal band (C-4), and a plain clamp employing a round-head machine

screw and square nut for clamping (C-2). The two screw clamps connected

the hose specimens to the manifold, and the banded and plain clamp con- nected them to the U-fittings.

^ ASTM D1418-77 designations for rubbers [1].

5
s

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C4

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C •' Hose damps (see text for types)

E “ Heat exclianger

F ’ Hose nipples, 16 mm 0.0.

H - Hose specimens, 350 mm

! - Inlet manifold

0 “ Outlet

i » Suspended mass

P “ Pump

IR - Reservoir

S - Supply plug

T - Thermocouples

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Figure 1. Schematic of circulatory system

HOSE LOOP

'I

6
The inlet manifold is connected to a heat exchanger with the 20-mm hose.

The outlet manifold is connected to the input of a centrifugal pump.

The output of the pump is directly connected to the heat exchanger. The

heat exchanger consists of a coil of 6o35-mm tubing about 3 m in length

brazed or welded into a cylindrical vessel having a capacity of about

1100 cra"^. For heating, steam is passed through the coil. For cooling,

chilled water or alcohol cooled with liquid nitrogen is passed through

the coil. A reservoir pressurized with laboratory air supply is con- nected to the inlet manifold.

Thermocouples are inserted into the heat exchanger, the outlet manifold,

in the alcohol bath, and on the copper steam line, which is also used

for the chilled water.

3.2.2 Procedure

The assembled circulatory system was filled with ethylene glycol-water

mixture containing 55 percent glycol by volume. The system was evacuated several times during the filling operation to remove all air except

that in the reservoir. The system was evacuated through the reservoir.

If air was not removed, fluid flow was restricted through one or more

hose loops. About 3500 cm^ of fluid was required to fill the brass and

copper system and about 4000 cm'^ was required to fill the steel system.

After the system was filled with fluid, the reservoir was pressurized

with air at 125 to 150 kPa (laboratory line pressure) and the air supply

was closed during heating. The air supply remained open during cooling.

The pump was started and steam was passed through the heat exchanger.

When the temperature of the circulating fluid reached 100°C, the flow

was regulated to maintain this temperature within 2°C. The pressure

increased about 100 kPa when the temperature was raised. Monday through

Friday the temperature was reduced once a day by circulating chilled

water (7 ^ 1°C) or alcohol chilled with liquid nitrogen through the

heat exchanger. Alcohol cooling to about -40°C was used generally twice

a week and chilled water cooling to about 10°C on the other 3 days. The

cooling cycle took about 4 to 5 hours. Nights and weekends, the temperature was maintained at 100°C.

The system was examined for leaks every work day and clamps were tightened

if leakage occurred. The fluid level in the reservoir was measured about

twice a week and additional glycol-water mixture added to keep the reservoir about half full. Any hose that failed was replaced and the test was continued by repeating the filling operation above.

3 Note: In the early part of the performance test, liquid nitrogen was passed directly through the heat exchanger coil. The fluid surrounding

the coil froze and the lowest temperature of fluid in the hoses was about -25°C. The use of chilled alcohol o^vercame this difficulty and

temperatures of -40°C or slightly below were obtained.

7
Temperatures were measured frequently during the cooling cycle and during

heating until the temperature is regulated at 100°C. Temperature was stable at nights and weekends unless a hose failure occurs and fluid was lost, but the pressure decreased due to leakage of air or fluid.

3.2.3 Results

The performance test covered a period of 5183 hours (slightly over 7 months). During almost 82% of this period, the temperature of the

fluid was about 100°C. Over 2% of this period was devoted to cooling

with liquid nitrogen to temperatures around -25“C during the early part

and to -40°C for most of the period. The temperatures during the remaining 16% of the period were between 10 and 25°C, which included the time

required to replace hoses, examine the fluid, stop leaks, etc.

Table 2 lists the 12 hoses, their dimensions, the number of specimens

that failed, and the number of leaks that occurred at the connections

The table combines the results of the two circulatory systems. Thus,

there are two clamps of each type, one in each system. Leakage occurs

at the connections with all four clamps, but much more frequently with

the plain clamp (C2), The lowest number of leaks with the banded clamp

(Cl) connections is misleading since this clamp is not adjustable and

leaks must be stopped with another clamp. The type of clamp does not seem critical since no leak occurred at the connections of hoses 6

and 9. The inner tube of hose 6 vulcanizes to the nipple and is very

difficult to remove at the end of test. The lining tears and rubber

still adheres to the nipple. Leakage at the connections of the VMQ

hoses seems to be related to the bore diameters. Hose 9 is free of leaks

at connections and has the smallest bore. The largest bore and greatest

number of leaks occurs with hose 10; in fact, this hose fits loosely on

the nipple. Surprisingly, the screw clamp with internal band does not seem to be better than the regular screw clamp in preventing leaks with

either EPDM or VMQ hoses. Hose 7 with a CR cover hardens and stiffens

during test so that it is difficult to stop leaks at the connections.

The leaks apparently develop from differential thermal expansion and

contraction of the hose and nipple, and the high compression set of the

hoses to be discussed later.

Hoses 3, 4, and 5 deteriorated rapidly under the conditions of this test;

all of the original specimens failed and in the case of hose 4, some replacement specimens also failed. Two of the four specimens of hose

2 and one specimen of hose 10 also had to be replaced. Possible cause

of these failures will be discussed under bursting tests in 3.6.

Substantial loss in fluid occurred that could not be entirely ascribed

to leakage at the connections. Measurement of the density of the fluid

in the circulatory systems revealed an increase in the glycol concentration from the initial 55 percent to about 70 percent. Thus, it was evident that water vapor was transmitted through the walls of some or

all hoses. Separate laboratory tests for water vapor transmission were

made which are discussed later.

8
Table 2. Hose Dimensions

,

Specimen Failures and Leaks at Clamps

Hose Type Bore Wall Specimens Leaks at Clamps^ mm mm No. failed Cl^ C2 C3 C4

EPDM 15.8 3.9 0 1 14 3 1

2 EPDM 16.2 4.3 2 1 20 5 4

3 EPDM 15.0 4.2 4 0 3 0 1

4 EPDM 15.4 3.8 6 0 4 1 1

5 EPDM 15.4 4.0 4 3 21 1 7

6 EPDM 15.5 5.1 0 0 0 0 0

7 ^ CR^ 15.1 5.0 0 2 32 1 2

8 VMQ 16.0 4.3 0 0 0 0 4

9 VMQ 15.7 4.8 0 0 0 0 0

10 VMQ 16.9 5.2 1 2 - 4 2

11 PTFE 16.2 1.7 0 e e e e

12 EPDM 19.9 4.6 0 - - - 5

^ Cl - Banded clamp ; C2-Plain clamp; C3-Screw clamp ; C4 -Screw

clamp with internal band.

^ When a leak occurred at a banded connection, a screw clamp was applied adjacent to the band.

^ Hose was purchased locally. Other hoses were supplied by the

manufacturers.

^ CR cover; type of rubber in lining is not known.

Special fittings are required with the stainless steel braided

hose. None of these connections leaked.

9
3.3 OZONE RESISTANCE

Rubber components in outdoor service frequently crack and fail from ozone

in the atmosphere. Therefore, it is important that the outer rubber

cover of hose used in solar energy systems have good ozone resistance.

3.3.1 Procedure

The procedures in ASTM D 380 and D 1149 were used. The 12 hoses were exposed in an ozone chamber having an ozone partial pressure of about

100 mPa (100 parts per hundred million at an atmospheric pressure of

100 kPa). The temperature of the chamber was maintained at 40®C. Hose

specimens about 350 mm in length were bent in a semicircle and held in

place by inserting the ends over aluminum plugs 16 or 19 mm in diameter

which were centered 230 mm apart on an aluminum plate. After exposure

in the chamber for 166 hours, the specimens were examined for cracks.

3.3.2 Results

Numerous cracks were visible on the edge of the CR (neoprene) hose in

tension. No cracking was observed in the other hoses.

3.4 COMPRESSION SET

The ability of a clamp to maintain a seal at a hose connection depends

on the clamp maintaining pressure on the hose at both high and low temperatures. Rubber under compression takes a set. Usually, this property

is measured on rubber alone. For solar energy systems, the compression

set of the composite hose is important. Therefore, modifications in

the standard test are necessary.

3.4.1 Procedure

ASTM D 395 was modified as follows: A specimen of hose about 50 mm in

length was used. An aluminum plug either 16 or 19 mm in diameter was placed in the bore and the outside diameter was measured. The specimen

was placed in the compression clamps shown in Figure 2 and the bolts were tightened to compress the walls of the hose 25 percent. The com- pression apparatus was then placed in an oven at 100 + 1°C and allowed

to remain for either 94, 166 or 190 hours. After removing the apparatus

from the oven, the bolts were released and the outside diameter of the

hose under the clamps was measured after 30 minutes.

3.4.2 Calculations

Compression set was calculated by the following equation:

r = 100 (A - B)

A - D

10
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1—r

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c

1

o o

T

B

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A > 5R, minimum

B - 25 mm

C - 10 mm + R, minimum

D - Holes to clear bolts

E - 3/8 O.D. + 1/8 I.D. of hose, maximum

R - 1/2 O.D. of hose, minimum

Figure 2. Compression clamp (two required]

11
where C = compression set in percent of compression

A * initial outside diameter of hose with plug

B = outside diameter of hose with plug after recovery

D = outside diameter of hose with plug during compression.

3.4.3 Results

At the end of the period in the oven, the bolts in the apparatus having

a CR or EPDM specimen were loose indicating 100 percent compression set.

There was no recovery during the 30-minute cooling period, as can be

seen from the results in Table 3. The VMQ hoses 8 and 9 had high set,

but there was still some compression stress on the hose when they were removed from the oven in the 96 h and 166 h tests. VMQ hose 10 was

the only one with low compression set. A high resilience EPDM hose

was received from one of the manufacturers after the performance test was completed. This hose was under considerable compression stress when

removed from the oven, and was comparable to the VMQ hoses in compression set.

3.5 WATER VAPOR TRANSMISSION

Since the performance test indicated water vapor transmission through

the walls of some or all of the hoses, a separate test for this property

was made. Since there is no standard method at the present time, the

follov/ing method was used.

3.5.1 Procedure

Hose specimens about 350 mm in length were used. Metal plugs either 16 or 19 mm in diameter were inserted in one end of the hoses, and clamped

with a screw clamp. The hoses were filled to about 80 percent of their

capacity v/ith water and the other end plugged so that the distance

between the metal plugs was 300 mm. Screw clamps were then fastened to

this end. The masses of the assembled hoses and of equivalent lengths

of hose used as blanks were determined. The two sets of hoses were

pla ced in an oven at 100 + 1°C. The masses of the hose were determined daily except on weekends. The test was terminated after seven

days. After the oven test for water vapor transmission was completed,

the metal plugs were examined for corrosion. In tests 2 and 3, aluminum

plugs were used in both ends. In test 1, steel plugs were used in one end and on the other end brass plugs were used in the nominal 16-mra

hoses and a copper plug was used in the nominal 20-mm hose. In test 3

an ethylene glycol-water mixture was used containing equal masses of

each. The rate of water vapor transmission v/as determined by deducting

the loss in mass of the "blank" hose from the loss in mass of the

assembled hose containing fluid.

12
Table 3. Compression Set

Hose Type Compression Set at 100®C; - Percent

94 h 166 h 190 h

1 EPDM lOOf 100+ 100+

2 EPDM 100+ lOOh 100+

3 EPDM 100+ 100+ 100+

4 EPDM 100+ 100+ 100+

5 EPDM 100+ lOCH- 100+

6 EPDM lOCH- 96 100+

7 CR 93 100+ lOOf

8 VMQ 99 84 100+

9 VMQ 39 72 lOOh

10 VMQ 5 32 33

11 PTFE test is not applicable

12 EPDM lOCH- 100+ 100+

13^ EPDM 87

Compression set is over 100 percent.

^ Hose received after performance test on other hoses was completed.

13
3.5.2 Results

The results of the water vapor transmission tests are given in Table 4.

The lowest transmission rate occurs with hose 11 (PTFE). The highest

rates occur with the VMQ hoses. The ethylene glycol-water mixture in

these hoses in test 3 increases substantially in density, confirming

the experience in the performance test. The transmission rate for EPDM

hoses is generally less than 20 percent of that for the VMQ hoses, and

the increase in density of glycol-water mixture in EPDM hoses is about

15 percent of that in VMQ hoses.

The condition of the metal plugs at the end of tests 1 and 2 is given in

Table 5. Hose 10 causes pitting corrosion of the aluminum plugs, and

the VMQ hoses 8, 9 and 10 cause corrosion of the steel plugs. EPDM hoses

2 and 6 cause slight corrosion of the steel plugs. The metal plugs in

the other hoses range from clean to dark discoloration with no evidence

of corrosion. The condition of the water in the hoses at the end of test

1 is shown in the last column of Table 5.

In hoses where corrosion of the steel plugs occurred, the water has a dark brown rust color with sediment. It should be noted that distilled

water was used with no inhibitor in tests 1 and 2. The ethylene glycol

used in test 3 has inhibitor, so metal corrosion would not be expected

in a 7-day test. It is evident that the compounding materials in some hoses are likely to cause corrosion, and the compounding materials in

other hoses inhibit corrosion to some degree.

3.6 BURSTING PRESSURE

Hose used in solar energy systems must have sufficient strength to withstand fluid pressures in the system and provide a reasonable margin of

safety. Usually the minimum bursting pressure is required to be five

times the maximum working pressure. The hose must retain sufficient

strength for many years under service conditions. Accordingly, the

bursting pressures of the hoses are examined in essentially new condition and after completion of the performance test.

3.6.1 Procedure

The procedure in ASTM D 380 was followed, except the specimens were

about 350 mm in length. A hand operated hydraulic pump was used to

apply fluid pressure. The pressure was increased as rapidly as the pump

permitted.

Since there was insufficient material of some hoses to test unused hoses,

tests were made on specimens used in the water vapor transmission test.

The four specimens of each hose remaining from the performance test were

also tested. Some of these specimens were replacements and had only

short service exposure.

14
Table 4. Water Vapor Transmission at 100®C

i’

,1 Hose Type Vapor Transmission (g/day) Density®

Test 1 Test 2 Test 3^ kg/m^

1 EPDM — 0.57 0.66 1064

2 EPDM 0.48 0.46 0.46 1060

3 EPDM 0.67 0.70 0.61 1059

4 EPDM 0.81 0.80 0.71 1062

5 EPDM 0.80 0.80 0.92 1064

6 EPDM 0.48 0.46 0.55 1060

7 CR 1.43 1.74 0.82 1062

8 VMQ 5.31 5.23 3.51 1099

9 VMQ 5.30 5.03 3.48 1098

10 VMQ 4.71 4.92 3.43 1099

11 tfpe'^ 0.21 — — —

12 EPDM^ 0.89 0.91 1.06 1062

13 EPDM® 0.82 — — —

^ Density of glycol-water mixture after test 3. Original

density of mixture 1055 kg/ra^.

^ Ethylene glycol-water mixture (equal masses of each). Same

specimens as in test 2.

^ Stainless steel wire braid cover.

^ Nominal bore 20 mm; nominal bore of other hoses 16 mm.

^ High resilience EPDM hose submitted after completion of performance tests.

15
Table 5. Effect of Hose on Metal Plugs in Water Vapor

Transmission Tests (166 hours at 100®C)

Hose

12

3

4

5

6

78

9

10

11

12

13

Aluminum Brass

Test 2 Test 1

Steel Water

Test 1 Test 1

^ clean or nearly clean

^ very slight discoloration

^ slight discoloration

^ dark discoloration

® slight corrosion

^ corrosion

^ clear

slightly cloudy

slight sediment

slight rust color

y sediment

^ dark brown rust and

sediment

* The rust in the water came from iron pipe caps on this hose.

It was not feasible to use plugs with clamps in testing the

PTFE hose with stainless steel wire braided cover.

16
3.6.2 Results

Table 6 lists the bursting pressures in kilopascals. It is evident that

all rubber hoses lost strength in the performance test. The values for

hose 12 decreased from over 7500 kPa to less than 10 percent of the

initial value. The bursting values for hoses used in the water vapor

transmission tests tend to be lower than those subjected to the same heat in the dry condition (compare column a and b). The bursting values

for VMQ hoses tend to decrease less in the performance test than those

for other hoses. This difference in behaviour is apparently attributable

to the reinforcement materials in these hoses. Although the reinforcement in all hoses was not obtained, it appears that rayon fiber was used

in hoses that decreased in bursting strength greatly. This fiber is

known to deteriorate rapidly at high temperature in the presence of

moisture.

4. DISCUSSION

This study achieved the objective of determining the important requirements of hose used in solar energy systems. Laboratory tests are available to assess these requirements, except for deterioration of

reinforcement material. A short laboratory test is not adequate to assess this characteristic. However, the behaviour of fibers at various

temperatures in many environments is known or could be established.

Fibers which deteriorate extensively under service conditions in solar

energy systems should be precluded from use as reinforcement for hose.

Although some of the hoses survived the performance test without leakage

at the connections or failure, none is ideal for use with aqueous fluids

below 100°C in solar energy systems. The PTFE hose with stainless steel

braid is expensive and requires special fittings. It is recommended

for use in industrial systems operating at very high temperatures with

non-aqueous heat transfer fluids or pressurized aqueous fluids. The VMQ

hoses have a high transmission of water vapor through their walls. They

are not recommended for use with aqueous heat transfer fluids, but should

be useful with compatible non-aqueous fluids that do not pass through

the walls. The EPDM hoses tested have two weaknesses. The reinforcement

used in them deteriorates rapidly at high temperatures when transporting

aqueous fluids. They also have 100 percent compression set so that leakage at the connections is bound to be a problem. The high resilience

EPDM hose that was submitted later should overcome these weaknesses.

This hose has knit aramid reinforcement, so it should be suitable for

transporting aqueous heat transfer fluids. However, the knit construction may not withstand applications with repeated flexing and impulse.

The CR hose has the weaknesses of the EPDM hose plus two others. The

ozone resistance of this hose is not adequate for use in solar energy

systems and the hardening and stiffening that occurs in service makes

leakage at the connections difficult to stop.

The performance of hose 6 which vulcanized to the nipples indicates

that adhesives could be used effectively to obtain leak proof connections. However a high resilience hose should not require an adhesive

17
Table 6. Bursting Pressures

Hose Type Bursting Pressures in kPa

a b c d e f

1 EPDM 2210 1240 1100 1240 970

2 EPDM 7000+ 5930 1100* 6620* 970 970

3 EPDM 2340 1240 1380* 830* 2000* 2340*

4 EPDM 3310 2620 1240* 830* — 1100*

5 EPDM 3030 2620 2260* 1380 2380* 830

6 EPDM 7000+ 7000+ 3100 6760 2140 2620

7 CR 6070 6270 2340 2070 1720 970

8 VMQ 2480 1930 1380 2480 1650 1310

9 VMQ 4830 4270 4410 3450 3720 3720

10 VMQ 7500+ 7500+ 4900 5790 5790 6760*

11 PTFE not tested

12 EPDM 7500+ 7500+ 550 ““ 690 —

13 EPDM 3450 3450 .Ml

^ Specimens used as blanks and heated at 100°C for 166 h..

Specimen used for water vapor transmission and heated at 100°C

for 166 ho

^ Specimens connected to inlet manifold of brass and copper system.

^ Specimens connected to outlet manifold of brass and copper system.

® Specimens connected to inlet manifold of steel system.

^ Specimens connected to outlet manifold of steel system.

* Replacement specimens.

+ Specimen did not fall at this pressure.

18
to be leakproof. Further the type of clamp used is not critical if the

hose has high resilience, which offers promise in developing clamps easy

to install and reliable in service.

5. PROPOSED STANDARD

Based upon the results of this study, a proposed standard specification

for rubber hose used in solar energy systems has been prepared and is

given in the Appendix. This standard has requirements for the following

characteristics:

(1) Physical properties of inner tube and outer cover before and

after accelerated aging,

(2) Resistance to ozone of the outer rubber cover.

(3) Compatibility of the inner tube with the heat transfer fluid.

(4) Flexibility at low temperatures.

(5) Compression set of the composite hose.

(6) Bursting pressure of the composite hose.

(7) Vapor transmission through the hose walls of the heat

transfer fluid.

(8) Effect of hose on heat transfer fluid and metal.

(9) Reinforcement material.

Hose conforming to this standard should give good performance in solar

energy systems and not require maintenance when properly installed.

6. ACKNOWLEDGMENT

This project was supported by a grant from the Department of Energy.

Hoses for tests were supplied by Aeroquip Corporation, American Biltrite

Inc. , Dayco Corporation, Gates Rubber Company, and The Goodyear Tire and

Rubber Company. Advice was received from several members of ASTM Sub”

committee D-11.31 Rubber Hose. The Authors are indebted to these

organizations and to colleagues at the National Bureau of Standards for

their assistance in making this study possible.

7. BIBLIOGRAPHY

[1] 1978 Standards: Part 37 and Part 38, Rubber Products, Industrial

Specifications and Related Test Methods, published by the American

Society for Testing and Materials, 1916 Race Street, Philadelphia,

Pennsylvania 19103.

19
[2] Solar Energy Systems - Standards for Rubber Seals, Stiehler, R. D.

,

Hockman, A., Embree, E. J., and Masters, L. W. , NBSIR 77-1437 (1978).

[3] Measurement of the Aging of Rubber Vulcanizates , Mandel, J.

,

Roth, F. L. , Steel, M. N., and Stiehler, R. D. , Journal of

Research of the National Bureau of Standards, Vol 63C, pages 141

to 145 (1959).

20
APPENDIX

PROPOSED STANDARD SPECIFICATION FOR RUBBER

HOSE USED IN SOLAR ENERGY SYSTEMS

SCOPE:

1.1 This specification establishes quality requirements for rubber

hose used to convey liquids in solar energy systems to provide

producers, distributors, and users with criteria to evaluate

this product. Particular applications may necessitate other

requirements that would take precedence over these requirements

when specified.

1.2 An annex covers connections of rubber hose to the solar energy

system.

1.3 This specification does not include requirements pertaining to

the fabrication or installation of the hose.

1.4 This specification does not cover hose made from plastics.

APPLICABLE DOCUMENTS

2.1 ASTM Standards

D 380 Testing Rubber Hose

D 395 Test Method for Rubber Property —- Compression Set

D 1349 Rubber - Standard Temperatures and Atmospheres for

Testing and Conditioning

D 1566 Definitions of Terms Relating to Rubber

D 3832 Specification for Rubber Seals Contacting Liquids in

Solar Energy Systems

2.2 Other Standards

ISO 1307 Rubber Hose - Bore Sizes, Test Pressures and Tolerances on Length

ORDERING INFORMATION

Purchase orders shall include the following information:

3.1 Reference to this standard, ASTM xxxx

3.2 Inside diameter

21
3.3 Length

3.4 Type and Class (see 4.1 and 4.2)

1 i 3.5 Type of fluid to be conveyed.

3.6 Maximum service temperature

Note 1 “ This temperature normally occurs under stagnation

conditions and maximum radiation flux.

3.7 Maximum working pressure

3.8 Other requirements

4. CLASSIFICATION

4.1 Types

Type C, intended for use in cold climates (below -10*C in

winter

)

Type W, intended for use in warm climates (above -lO^C in

winter)

4.2 Classes

Class A, intended for use with aqueous fluids at 100*C or less

Class AT, intended for use with aqueous fluids above 100“C

Class N, intended for use with nonaqueous fluids

Note 2 ~ Aqueous fluids include water and antifreeze solutions.

5. TERMINOLOGY

5.1 Nipple - a cylindrical tubular attachment, one end of which is

securely inserted and retained in the end of a hose, to convey

fluid to or from the hose.

5.2 Definitions of other terms are given in ASTM D 1566

22
6 STANDARD SIZES

6.1

The following internal diameters are standard:

mm in

10.0 0.38

12.5 0.50

16.0 0.63

20.0 0.75

25.0 1.00

31.5 1.25

AO.O 1.50

50.0 2.00

Note 3 - The metric and inch sizes are not identical. The

metric sizes are based on the RIO series of preferred

numbers given in ISO 1307.

6.2 The internal diameter shall not exceed the specified value in

6.1

and shall not be less than this value by more than 1.5 mm

or 0.06 in for sizes of 20 mm or less, or 3.0 mm or 0.12 in

for sizes above 20 mm.

6.3 The tolerance on length shall be + 3 mm or + 1 percent of the

length whichever is larger.

7. REQUIREMENT

7.1 Construction - The hose shall consist of an inner tube, reinforcement and outer cover. The outer cover may be rubber or

a fibrous material (metallic or non-metallic) that is part of

the reinforcement. The inner tube and rubber cover shall be

smooth, uniform in thickness, and free from pitting, pinholes,

blisters and other defects.

Note 4 - Intentional pricks in rubber cover to allow vapors to

escape from reinforcement or lengthwise ribs on outer

cover are not considered defects.

7.2 Inner Tube and Outer Rubber Cover - These rubber components

shall comply with the requirements given in Table 1.

7.3 Hose - The composite hose shall comply with the requirements

given in Table 2.

7. A Reinforcement Material - The reinforcement shall be stable in

the presence of vapors of the heat transfer fluid at service

temperature as determined from the change in bursting pressure

of the hose in a prequalification test (see 9.3.2).

23
Table I.. Requirements for l^nner Tube and Outer Rubber Cover

PROPERTY

Ultimate elongation, min, %

Tensile strength, min, MPa

lb/ in^

Resistance to heating^

Change in ultimate elongation, max, %

Change in tensile strength, max, %

Resistance to heat transfer fluid^

Change in ultimate elongation, max, %

Change in tensile strength, max, %

Change in hardness, max Change in volume, max, %

Resistance to ozone of outer cover

100 mPa'^ for 166 h at 40°C

Resistance to low temperature

Type C hose only, "~40“C

REQUIREMENT

250

6o2

900

“40

“20

+25

+25

+10

+15

no cracking

no cracking

^ Class A hose shall be heated at 125 + 2 °C for 166 + 2 h. Class AT and

N hose shall be heated for 166 + 2 h at a standard temperature in ASTM

D 1349 between 25 and 49“C above maximum service temperature, but not

less than 125°C<. These test temperatures are; 125, 150, 175, 200,

225 and 250°C.

^ Inner tube of Class A and AT hose shall be immersed in a mixture con- taining equal volumes of ethylene glycol and water for 166 + 2 h at

100 + 2 °C. Inner tube of Class N hose shall be immersed in heat transfer fluid used in solar energy system for 166 + 2 h at a standard

test temperature in ASTM D 1349 next above maximum service temperature,

but not less than 100®C<> If the vapor pressure of the fluid is above

atmospheric pressure at the test temperature, the next lower standard

test temperature shall be used.

^ 100 mPa ozone partial pressure is equivalent to 100 pphm at standard

atmospheric pressure of 100 kPa.

24
Table 2. Requirement for Composite Hose

PROPERTY

Compression set, max, %

Bursting pressure, min

Vapor transmission rate, max, p g/(m*s)

Effect on aluminum, brass, copper and steel

Effect on fluid

Stability of reinforcement

maximum decrease in bursting

pressure, %

REQUIREMENT

85^

five times working

pressure

3^5b,c

no corrosion^

no sediment or dark

discoloration®

50

® Set is measured after conditioning under 25% compression for 166 + 2 h

at 100 + 2 “C for Class A hose and at standard test temperature in

ASTM D 1349 between 25 and 49°C above maximum service temperature, but

not less than 125“C (See footnote a. Table 1 for standard test

temperatures).

^ Equivalent to 0.9 g/day for a specimen having an internal length of

300 mm between plugs.

® The requirement for Class N hose with specified fluids should be agreed

between supplier and purchaser of hose.

^ Condition of plugs at the end of the test for vapor transmission rate.

Discoloration of plugs without corrosion is permitted.

® Condition of fluid at end of test for vapor transmission rate. Slight

cloudiness or slight discoloration is permitted.

I

1

25
The bursting pressure should decrease less than 50 percent for stable

material.

8. SAMPLING

8.1 The Inspection and test procedures specified are to be used to

determine conformance of products to the requirements of this

Standard. Each producer or distributor whose products are represented as conforming to this Standard may utilize statistically based sampling plans which are appropriate for each

particular manufacturing process and product characteristic.

Essential records shall be kept to document with a high degree

of assurance that all requirements of this Standard have been

met.

8.2 In case of dispute between purchaser and seller regarding quality,

five pieces of hose shall be taken from the lot at random and

those attributes in dispute shall be tested for compliance with

this Standard. If one piece does not conform, a second set of

five pieces may be taken and tested. If two or more of the

ten pieces do not conform, the lot may be rejected.

9. TESTING

9.1 Hose shall be tested according to ASTM D 380 for requirements

in Table 1.

9.2 Hose shall be tested for compression set and bursting pressure

by the following procedures:

9.2.1 Compression Set - Use the procedure for Method B in

ASTM D 395 except that the specimen shall consist of a piece of hose at least 50 mm in length and the compression plates shall have the curvature of the outside of

the hose as illustrated in Figure 1. Place a metal

cylinder having an outside diameter (A) equal to the

inner diameter of hose given in 6.1. Measure the outside diameter (B) of hose with cylinder in place. Place

specimen between compression plates and tighten bolts

until hose is compressed to 0.75B + 0.25A. Place the

apparatus in an oven at temperature given in footnote

a. Table 2 and leave for 166 + 2 h. Remove the apparatus

from the oven, loosen clamping bolts, and after 30

minutes measure the outside diameter (C) of hose at the

center of the clamping area. Calculate compression set

in percent of compression, which is AOO (B - C)/(B - A).

9.2.2 Bursting Pressure - Determine the bursting pressure in

accordance with ASTM D 380.

26
A - 5R, minimum

B - 25 mm

C - 10 mm + R, minimum

D ' Holes to clear bolts

E - 3/8 O.D. + 1/8 I.D. of hose, maximum

R - 1/2 O.D. of hose, minimum

Figure I. Compression clamp (two required]
9.3 Prequalification tests of hose shall be nuade for vapor

transmission rate, effect on metals and fluid, and stabilit}'

of reinforcement. These tests shall be made for each rubber

composition and reinforcement material for initial qualification of hose design, and are not required for quality control

ol uuinuf acture. The following procedures shall be used:

9.3. 1 Vapor Transmission Rate and Effect on Metals and fluid

Prepare metal plugs from aluminum, brass, copper, and

steel 50 mm in length from rods having a diameter equal

to the inner diameter of hose given in &.I. Cut six

hose specimens 350 mm in length. Place an aluminum

plug in one end of one specimen to a depth of 25 mm

and clamp. Place a brass plug in second specimen and

clamp. Place a copper plug In third specimen and clamp.

Place a steel plug In fourth specimen and clamp. Fill

these specimens with the heat transfer fluid used in

Class N hose or water (Class A or AT hose), to about

75 mm of open end. Insert aluminum plug in first specimen, brass plug in second specimen, copper plug in third

specimen, and steel plug in fourth specimen, so that

distance between plugs is 300 mm, and clamp. Determine

the masses of the four hose assemblies and the two

specimens without fluid. Place the six hose specimens

in an oven at 100 + 1”C when testing Class A or AT hose,

and at a standard test temperature in ASTM D 1349 next

above the maximum service temperature, but not less than

100°C, when testing Class N hose. Determine the masses after 24 h and tighten clamps on specimens containing

fluid. Return the specimens to the oven for six more

days. Remove the specimens from the oven, allow them

to cool to room temperature, and determine their masses. Deduct the average loss in mass of the two dry specimens from the average loss in mass of the four specimens

containing fluid. Calculate the vapor transmission rate

in pg/(m’s). Disassemble the four hose assemblies and

examine the condition of the fluid and plugs.

9.3.2 Stability of Reinforcement - Cut ten hose specimens

approximately 350 mm in length. Insert hose nipples in

the ends of five specimens and clamp. Connect one nipple of each assembly to a fluid reservoir of about

100 cm^ capacity. Fill the hose and reservoir through

the other nipple with the heat transfer fluid used in

Class N hose or water in tests of Class A or AT hose

to about 90% of capacity. Close the filling nipple by

any suitable means and place the five hose assemblies

in an oven at 100 + 2°C when testing Class A or Class

AT hose, and at a standard test temperature in ASTM D

1349 nearest the maximum service temperature, but not

less than 100®C, when testing Class N hose. Examine

28
the fluid level in the assemblies after two and four

months, and add fluid if the level has decreased belovj

80% of capacity. After six months, remove the specimens

from the oven, disconnect the reservoirs, and measure

the bursting pressure 6f each specimen, including the

five specimens that were not filled and heated with

fluid. Calculate the change in average bursting pressure of the two sets of specimens as a percent of the

bursting pressure of specimens not heated.

10. MARKING

10.1 Name, brand or trademark of manufacturer.

10.2 Type and class.

10.3 Reference to this standard, ASTM Dxxxx.

10.4 Other information required by manufacturer or purchaser.

11. PACKAGING

11.1 Hose shall be protected by suitable packaging to prevent

damage during shipment or storage prior to installation in

solar energy system.

12. INSTRUCTIONS

12.1 Installation instructions should be included with each package. The Annex gives guidance on information to be included

to assure long leak-free service. Instructions are not necessary for hose supplied with end fittings unless special precautions during installation or maintenance procedures must

be followed.

29
ANNEX

Al. CONNECTION OF HOSE TO SOLAR ENERGY SYSTEM

The means for fastening the hose to components in the solar energy

system is critical. The two mechanisms commonly employed are through end fittings on the hose or clamps. Materials that resist

corrosion is essential. The following provisions are general

requirements and not complete specifications for these connections.

A. 1.1 Hose Nipples - Outside diameter shall be not less than the

specified value in 6.1 and shall not exceed this value by more than 3 mm, including serrations or enlargement to prevent slippage.

A. 1.2 End Fittings - Hose equipped with end fittings shall withstand a minimum tensile force of 1.3 kN(300 lb). In the

bursting pressure test (9.2.2), the hose shall not move out

of the end fittings more than 1.6 mm (0.06 in). Rubber

seals in end fittings shall comply with ASTM D 3832. The

design of the end fitting shall be agreed between purchaser

and supplier.

A. 1.3 Clamps - Hose intended for use with clamps shall be shipped

with instructions for proper clamping to prevent slippage of

hose from the connecting tubes in the solar energy system

and cutting of the hose by the clamps. The instructions

should emphasize that one or more ridges between the clamp

and end of hose nipple is essential to prevent slippage,

that the clamps should have a wide surface to support the

clamping forces without cutting of the hose. The instructions should also include recommendations for use of adhesives to prevent leakage and reduce or eliminate maintenance

during long service.

A. 1.4 Compatibility - The rubber hose, metal components and circulating fluid should be compatible in order to minimize metal

corrosion and deterioration of rubber hose and fluid. Specifications for compatibility beyond the provisions in Table 2 and 9.3 should be agreed between purchaser and seller.

A. 1.5 Expansion Joints - Hose connections in solar energy systems

that also serve as expansion-contraction joints should be

designed so that straight hose acccomodates motion by flexure

and not by axial compression and tension. Hose made with one

or more bellows to accomodate axial compressive and tensile

movement should accomodate the maximum motion likely to occur

under extreme service conditions without placing significant

stress on the components connected.

30
MBS-114A (REV. 9-70)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 79-1917

4. TITLE AND SUBTITLE

Solar Energy Systems - Standards for Rubber Hose

I'HWiwf ww y

^ V. . S . 1

'

iVlVlYl^'i'l 5. Publication Date November 1979

7. AUTHOR(S)

Robert 0. Stiehler and John L. Michalak

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS fSfrooj. city, Sfate, ZIP)

Department of Energy

Office of the Assistant Secretary

Conservation .and Solar Applications

20 Massachusetts Avenue

Washington, DC 205?5

13. Type of Report & Period Covered

15. SUPPLEMENTARY NOTES

|~1 Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 20(h\vord or less factual summary of moat significant infonnation. If document includes a significant bibliography or

literature survey, mention it hers»)

A study of commercial rubber hose was made to develop standards for hose ised in

solar energy systems. Twelve hoses were evaluated by cycling between temperatures

of about 100 ^C and temperatures as low as -40 ”C during a period of about seven

months. Laboratory tests for bursting strengths compatibility with metals,

compression set, ozone resistance, and water vapor transmission were also made.

The results of this study and tests are presented. Based on these findings, a standard for rubber hose used in solar energy systems is proposed.

17, KEY WORDS (six to twelve entriee; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons)

Hose; hose specifications; rubber hose; solar energy systems

18. AVAILABILITY Unlimited

I I For Official Distribution. Do Hot Release to NTIS

I I Order From Sup. of Doc., U.S. Government Printing Office, Washington, DC

20402, SD Stock No. SN003-003- ^ Order From National Technical Information Service (NTIS), Springfield,

VA. 22161

19. SECURITY CLASS 21. NO. OF

(THIS REPORT) PRINTED PAGES

UNCLASSIFIED

35

20. SECURITY CLASS 22. Price (THIS PAGE)

$4.50

UNCLASSIFIED

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